The present invention relates to a method of regulating a steam injector of the type which has an inlet for steam and an inlet for the product which is to be heat-treated, as well as an outlet for the ready-treated product, the steam injector further having concentrically disposed gaps for steam and product, the gaps being capable of being regulated in that a centrally disposed regulator spindle is protracted or retracted reciprocally.
Heat-treating liquid foods such as milk or juice in order to render them aseptic results in a product which remains stable on storage at room temperature. The aseptic product contains no harmful micro-organisms which can grow during storage, and no unbroken refrigeration chain is needed for distributing the product, which may be an advantage above all in the developing countries.
There are different methods of heat-treating foods, of which two main groups may be distinguishedxe2x80x94indirect and direct heating. The indirect methods consist of treatment in various types of heat exchangers. Of the direct methods, mention might be made of treatment using steam in an injector and heating by means of infusion.
All methods of heat-treating today strive for as gentle a heating as possible in order to avoid deterioration in the flavour of the product, at the same time as the method must be both effective and reliable. The direct methods thereby offer a more rapid heating of the product, with the result that it is possible to reduce the treatment time. By such means, an overall reduced thermal effect on the product is achieved, which entails that the product receives a gentler treatment as far as the flavour is concerned.
The present invention relates to a method which is applicable to an injector, which entails that a reliable and effective treatment of the product is obtained. An injector of the type which is contemplated here is described in Swedish Patent Specification SE 367 121. The injector, which is of the so-called annular gap type, has an inlet for steam and an inlet for product. Product and steam are distributed in different concentric gaps around a regulator spindle and converge together, a condensation of the steam in the product being obtained.
In order to obtain an effective condensation of the steam in the product, a constant pressure difference must be maintained over the injector. The prior art injectors had a key grip in order to make for regulation of the position of the regulator spindle in the injector, which, however, entailed that careless or unskilled regulation would result in incomplete condensation. A certain minimum pressure drop must exist, since otherwise rapid and exaggerated pressure and temperature oscillations would occur, with the result that no reliable heat-treatment is achieved. Moreover, a certain minimum pressure drop is a mandatory requirement placed by the authorities in certain countries.
The injectors available on the market today are most generally set at fixed capacities by means of replaceable spacer washers. However, this is a disadvantage since it is not possible rapidly and simply to regulate the capacity of the injector. The need to be able to regulate the capacity of the injector exists, for example, in the event of loss of a filling machine during production or in the event of product change if there is no sterile tank acting as a buffer in the plant. In, for example, the loss of a filling machine in the plant, it is at present necessary to recirculate the excess product over the plant, with a deterioration in the product quality as a result.
One object of the present invention is therefore to realise a method of simply and reliably regulating the gaps in a steam injector, while maintaining a constant pressure difference over the injector.
This and other objects have been attained according to the present invention in that the method of the type described by way of introduction has been given the characterizing feature that the regulator spindle is regulated by means of switching device, the switching device being controlled by the pressure difference between a pressure measured in the product inlet and a pressure measured in the product outlet.
One preferred embodiment of the method according to the present invention has further been given the characterizing features as set forth in the appended subclaims.